<template>
  <ul class="list">
      <li 
        class="item"
        v-for="item of letters"
        :key="item"
        :ref="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
      >
      {{item}}
      </li>
  </ul>
</template>

<script type="text/javascript">
export default {
  name: 'CityAlphabet',
  props:{
    cities : Object
  },
  computed:{
    letters(){
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data(){
    return {
      touchStatus:false,
      startY : 0,
      timmer :null
    }
  },
  updated(){
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods:{
    handleLetterClick (e){
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart(){
      this.touchStatus = true
    },
    handleTouchMove(e){
      if ( this.touchStatus) {
          if (this.timmer) {
            clearTimeout(this.timmer)
          }
          this.timmer = setTimeout(() => {
              const touchY = e.touches[0].clientY - 79
              const index = Math.floor((touchY - this.startY) /20)
              if (index >= 0 && index < this.letters.length) {
                this.$emit('change',this.letters[index])
              }
          }, 16);

        
      }
    },
    handleTouchEnd(){
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
@import  '~styles/varibles.styl'
.list
  display flex
  flex-direction column
  justify-content center
  position absolute
  right 0px
  top 1.58rem
  bottom 0px
  width .4rem
  .item
    text-align center
    line-height .44rem
    color $bgColor
</style>
